Following edge emitting lasers, vertical cavity surface emitting lasers (VCSELs) have emerged as an important electro-optical converter for producing laser light. VCSELs emit the laser light towards their vertical cavity surfaces at a small angle, providing ease of integration and arrangement, and therefore VCSELs are especially suitable for use as a high density emitting device and as a communication bus between chips. However, conventional VCSELs require multilayer-distributed Bragg reflectors (DBRs) which utilize a material different from the active layers, such that fabrication of the conventional VCSELs is very complicated. In addition, the electro-optical conversion efficiency of the conventional VCSELs is also limited due to high internal resistance induced by the reflectors.
On the other hand, the conventional VCSELs are able to emit laser light of a single wavelength and unable to obtain a plurality of wavelengths in one device. Therefore, in some applications, it is necessary to use a plurality of VCSELs producing various wavelengths in order to obtain a plurality of wavelengths. As a result, not only are the VCSELs fabrication costs increased, but also their integration is not good enough to reduce density.